Scrolls are enchantments that you can apply to blue/purple equipment that does not have an enchantment already applied.

If you have a character with blue/purple kit equipped, click on the item in their inventory, then on the menu on the right hand side should be an 'Enchantment' option (alongside the Shop option that lets you buy equipment direct from the shop onto the character)

Different enchantments are for different item types: I think the breakdown is